LANCE FLORA OF EASTERN WYOMING 101 



Table l~-Leaf characters of dicotyledons, showing relative percentages in each category 



Flora 



Margin 



Entire 



Xon- 

 entire 



Length 



Over 

 10 cm. 



Under 

 10 em. 



Venation 



Pinnate 



Palmate 



Texture 



Thick 



Thin 



Temperate: 

 Muir Woods, 22 species (modern) 

 Bridge Creek, 20 species 



Warm temperate to subtropical: 



Weaverville, 36 species 



La Porte, 35 species 



Hell Creek, 28 species 



Lance, 46 species 



Medicine Bow, 42 species 



Sublropical lo iropical: 



Laramie, 55 species 



Goshen, 49 species 



Panama, 41 species (modern) . . . . 



23 

 15 



47 

 71 

 54 

 54 

 67 



71 

 61 



88 



77 

 85 



53 

 29 

 46 

 46 

 33 



29 

 39 

 12 



27 

 30 



60 

 35 

 36 

 41 

 45 



45 

 53 

 56 



73 



70 



40 

 65 

 64 

 59 

 55 



55 

 47 

 44 



77 

 70 



60 

 65 

 64 

 54 

 60 



64 



82 

 83 



23 

 30 



40 

 35 

 36 

 46 

 40 



36 

 18 

 17 



64 

 55 



57 

 83 

 64 

 67 

 71 



73 

 98 

 98 



36 



45 



43 

 17 

 36 

 33 

 29 



27 

 2 

 2 



and the essentially subtropical Medicine Bow. In texture and venation characters 

 they are only 4 per cent and 6 per cent, respectively, out of accord with the Medicine 

 Bow flora. In their combined characters the Lance species are closest to those of 

 the Medicine Bow flora, which is considered intermediate between warm temperate 

 and subtropical, more nearly approaching the latter. In view of the usual difficul- 

 ties of definition it may be said that the leaf characters of the Lance species indicate 

 climatic conditions intermediate between warm temperate and subtropical, more 

 nearly approaching the former. 



As the data of table 1 were being arranged, it became apparent that the per- 

 centages representing the Lance, Medicine Bow, and Laramie leaf characters fall 

 rather precisely into a steady progression. In terms of chmatic conditions this is 

 interpreted to mean that the Lance conditions were somewhat more temperate than 

 those of the Medicine Bow, which in turn were somewhat more temperate (or less 

 subtropical) than those of the Laramie. Since these three floras are essentially con- 

 temporaneous and occupy progressively more southerly positions in latitude, such 

 an observation is rather to be expected in view of latitudinal control of vegetational 

 zones. It was consequently a natural step to determine whether or not the con- 

 temporaneous Colgate-Hell Creek flora, from a region lying north of the Lance 

 deposits, would fit into this progression. This it does to a large degree, as is shown 

 in table 1. In length, texture, and marginal characters the Colgate-Hell Creek 

 species indicate, as anticipated, a sHghtly more temperate aspect than the Lance 

 species. A considerable discrepancy is to be noted, however, in venation charac- 

 ters, which are the same in the Colgate-Hell Creek species as in the more sub- 

 tropical Laramie species. I can offer no suggestion as to the real meaning of this 

 discrepancy. It must be noted, however, that there is another inexphcable anomaly 

 in this column of table 1, namely, the abnormaUy high percentage of pinnately 

 veined leaves in the temperate Muir Woods and Bridge Creek floras. 



